Using Sequel I'd like to join two subqueries together that share some column names, and then table-qualify those columns in the select.
I understand how to do this if the two datasets are just tables. E.g. if I have a users table and an items table, with items belonging to users, and I want to list the items' names and their owners' names:
@db[:items].join(:users, :id => :user_id).
select{[items__name, users__name.as(user_name)]}
produces
SELECT "items"."name", "users"."name" AS "user_name"
FROM "items"
INNER JOIN "users" ON ("users"."id" = "items"."user_id")
as desired.
However, I'm unsure how to do this if I'm joining two arbitrary datasets representing subqueries (call them my_items and my_users)
The syntax would presumably take the form
my_items.join(my_users, :id => :user_id).
select{[ ... , ... ]}
where I would supply qualified column names to access my_users.name and my_items.name. What's the appropriate syntax to do this?
A partial solution is to use t1__name for the first argument, as it seems that the dataset supplied to a join is aliased with t1, t2, etc. But that doesn't help me qualify the item name, which I need to supply to the second argument.
I think the most desirable solution would enable me to provide aliases for the datasets in a join, e.g. like the following (though of course this doesn't work for a number of reasons)
my_items.as(alias1).join(my_users.as(alias2), :id => :user_id).
select{[alias1__name, alias2__name ]}
Is there any way to do this?
Thanks!
Update
I think from_self gets me part of the way there, e.g.
my_items.from_self(:alias => :alias1).join(my_users, :id => :user_id).
select{[alias1__name, t1__name]}
seems to do the right thing.